1. Field of the Invention.
The invention described and claimed herein is generally related to motorcycles. More particularly, the present invention is related to suspension and steering systems for the front wheel of a motorcycle.
2. Description Of Related Art Including Information Disclosed Under 37 CFR 1.97-1.99
For almost a century motorcycles have had a front suspension system consisting of a pair of telescoping fork tubes, to which the front wheel is journalled. The fork tubes typically contain internal spring and damping elements which absorb weight and shock loads on the front wheel. The fork tubes are typically connected at a steering head assembly, which is in turn connected to steering column that is journalled to the motorcycle frame and connected to the handlebar.
Despite the longstanding use of telescoping front fork tubes, there are well known disadvantages which are inherent in their design and use, and which cannot be entirely avoided. For example, there is the well known tendency for the motorcycle to "dive," or pitch forwardly and downwardly on hard braking. This results in an unsafe performance characteristic, particularly when it becomes necessary for a rider to brake hard while negotiating a curve.
Another design weakness derives from the fact that the fork must be extended forwardly at a "rake angle." One reason for extending the fork at a rake angle is to absorb road shocks caused by bumps, holes and other road irregularities. Road shocks caused by such obstacles have a substantial upward component of force, and in addition have a modest rearward component of force. Consequently it is desirable to extend the telescoping fork tubes at a rake angle that approximates to some extent the typical net direction of shock forces arising from road obstacles. A rake angle is also necessary to obtain a satisfactory steering bias, which is the bias that makes the motorcycle most stable with the front wheel in the straight, or unturned position; and which causes the front wheel of the motorcycle to tend to return the straight position from a turned position.
The design weakness arising from the extension of the forks at a rake angle arises from the fact that the weight load on the front wheel is a purely vertical force. As a result the internal fork seals are continuously subject to lateral stresses due to the weight load borne by the angled fork tubes, while they are also required to accommodate telescopic sliding motion of the fork tubes. This results in friction and wear of the fork tube seals.
Turning to another design aspect of motorcycles, it will be appreciated that in the conventional fork tube suspension the steering function and the suspension function are combined in the same fork tube suspension system. The result is that all weight and shock loads on the front wheel must be borne by the fork tubes, by the associated steering column, and by the head frame assembly. This results in these components of the steering system being made considerably stronger and having a considerably greater weight than would be necessary just to steer the motorcycle. Moreover, this excess weight is located high on the motorcycle and is spaced significantly from the center of gravity of the motorcycle, and as a result has an adverse effect on weight distribution and performance.
Consequently it has been recognized for some time that it would be desirable to separate the steering function from the suspension function, in much the same manner as these functions are routinely separated in automobiles and other four-wheel vehicles.
The inventor has previously disclosed a one-sided front suspension and steering system for a motorcycle, in U.S. Pat. No. 4,526,249, entitled "Front Suspension System for a Motorcycle," issued Jul. 2, 1985. That system overcomes many of the problems adverted to above. While that system has been successfully incorporated into a successful, commercially available motorcycle design, it has been limited in its application to relatively large "sport-cruiser" motorcycles, by the fact that the one-sided front arm of the suspension system is placed low on the motorcycle in order to permit its connection to the lower end of a kingpin member that supports the front wheel. As a result, the arcuate curve of the lower arm must be constructed quite large in order to accommodate the necessary range of steering motion of the wheel at its widest point. Moreover, the size of the front brake disk, which is located inside the kingpin, is to some extent limited by the size of the wheel and the space necessary to locate a brake caliper unit between the brake disk and the wheel rim.
Accordingly, it is the object and purpose of the present invention to provide an improved suspension and steering system for the front wheel of a motorcycle.
In this regard, it is also an object and purpose of the present invention to provide a front suspension system based on a one-sided swing arm mechanism, by which weight and shock loads are conveyed in a direct mechanical path between the front wheel and the center of mass located in the body of the motorcycle.
It is another object and purpose of the present invention to provide a front suspension system based on a swing arm mechanism that achieves the foregoing objectives and which also provides a wide angular range of steering motion to the front wheel.
It is yet another object and purpose of the present invention to achieve the foregoing objects and purposes in a front suspension system that has an improved capacity to utilize a conventional disk brake system.